There is a report on the development of a reflective type color TFT-LCD using a vertically aligned (VA) liquid crystal, having high reflectance (42%) and a high contrast ratio (80:1) (Non-Patent Document 1). This Non-Patent Document also reports that an MVA (Multi-domain Vertical Alignment) liquid crystal has been adopted as the VA liquid crystal and a low-cost reflective type color TFT-LCD having high display performance has been successfully implemented using a wrinkle diffusing reflective electrode through a newly developed photomask-less process.
This wrinkle diffusing reflective electrode is formed as follows. A photosensitive resin layer is formed on a TFT substrate, exposure to light is performed using a photomask for forming contact holes, and the photosensitive resin layer is developed to form contact holes. Next, the remaining resin is irradiated with UV light without any photomask. In this case, a shrinkage ratio distribution is formed in a single layer of photosensitive resin by adjusting UV intensity and spectral characteristics to make the shrinkage ratio of its lower layer greater than that of its upper layer. Then, a baking process is performed to shrink the resin having a shrinkage ratio distribution in the thickness direction, and to form wrinkle-shaped projections and depressions on the surface, and finally a metal layer having high light reflectance such as Al is formed on these wrinkle-shaped projections and depressions to manufacture a diffusing reflective electrode having a wrinkle-shaped surface similar to the projections and depressions.
This Non-Patent Document also refers to control of a reflective characteristic in a direction of the wrinkle-shaped projections and depressions. This refers to the fact that it is possible to make incident light to be reflected only in a specific direction by controlling a direction of the wrinkle-shaped projections and depressions. More specifically, a direction of the wrinkle-shaped projections and depressions is controlled by changing conditions of an interface between the photosensitive resin layer and the substrate to obtain directional reflection characteristics having high reflectance in vertical and horizontal directions.
However, this shape of the wrinkle-shaped projections and depressions largely depends on not only the thickness of the photosensitive resin and UV irradiation energy but also other various manufacturing parameters, and it is therefore assumed that it would not be simple to manufacture a desired shape reliably. Furthermore, even if optimum parameters are found and the product is manufactured according to these parameters, it is often the case where unexpected fluctuations of the parameters occur in the actual manufacturing flow, whereby the desired shape can not be formed stably, in particular variations among the products are easy to result.
[Non-Patent Document 1]
Norio Sugiura et al., ‘Reflective Color TFT-LCD using MVA Technology’, Liquid Crystal (EKISHO) Vol. 6, No. 4, 2002, Japanese Liquid Crystal Society, issued on Oct. 25, 2002, pp. 383-389